redhat: speed up userland-only rpm builds

redhat: speed up userland-only rpm builds

When building with --define "build_modules 0", have configure
skip the Linux kernel tests, which are slow and many.

Reviewed-on: https://gerrit.openafs.org/13239
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit ab61bcffefdd0a431a435def193cd9a46e3b8ab6)

Change-Id: I030c4fab62bc8973dd4d914374865569d878090d
Reviewed-on: https://gerrit.openafs.org/13248
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>